Coaxial line generator



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mi E amr! Filed Sept. 20, 1944 L. W. SCHREINER ETAL COAXIAL LINE GENERATOR m. IPN MM N w M l, mv .IQ 1 n a J f l :iL/M

Patented Jan. 11, 1949 COAXIAL LINE GENERATOR Louis W. Schreiner and Eugene V. Leonard, Philadelphia, Pa., assignors, by mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application September 20, 1944, Serial N o. 554,893

(Cl. Z50-36) Claims.

The present invention relates to high frequency apparatus, particularly oscillators and amplifiers for use in the medium frequency band.

An object of the invention is to provide a small, compact, co-mpletely shielded oscillator.

Another object is to provide an improved vacuum tube circuit unit for frequencies below those at which convenient operation may be obtained and compact equipment may be built in a cavity resonator, velocity modulated type of oscillator, but which will operate at frequencies far above those v at which ordinary tubes and lumped circuit constants may be employed.

An object of the invention is to provide high frequency apparatus, particularly useful in the range between 540 to 600 megacycles.

A more specific object of the invention is to provide a highly compact oscillator or amplifier which operates well in the frequency range such as 540 to 600 megacycles.

A further object of the invention is to provide a compact rigid circuit structure for use with electric discharge devices or vacuum tubes of the axially symmetrical type known as lighthouse tubes.

A further object of thev invention is to provide a circuit unit which is more compact than the conventional cavity for the frequency involved. It is also an object to provide an oscillating unit which provides greater stability than a circuit with transmission line elements.

A further object of the invention is to provide a high frequency generator which is axially symmetrical for the most part.

Other and further objects, features and ad vantages will become apparent as the description proceeds.

In carrying out thel invention in a preferred embodiment thereof, an electric discharge device or a space discharge device of the type known as a lighthouse tube is employed. A tank circuit is provided comprising an inner-conductor which may be a tube fitting the anode contact of the lighthouse tube and an outer hollow cylindrical conductor making contact with the cathode connection of the lighthouse tube, together with a capacity loading device for reducing the length of the physical dimensions of the resonant or tank circuit, and to provide a high current path to which the grid can be coupled to obtain proper feed-back.

For providing feed-back from the tank circuit to the grid circuit of the lighthouse tube, an inductive coupling loop is provided which makes contact with the grid of the tube and is coupled with respect to high frequency to the outer cylindri-cal conductor. The capacity loading for the tank circuit is positioned sufciently close to the inductive coupling loop for providing electromagnetic reaction between the capacity element or the dielectric electrostatic fiux therein and the coupling loop.

A. better understanding of the invention will be afforded by the following detailed description considered in conjunction with the accompanying drawing, and those features of the invention which are believed to be novel and patentable will abe pointed out in the claims.

The single figure of the drawing is a schematic diagram of one embodiment of the invention representingy a portion of the apparatus in longitudinal section.

For the sake of illustration the apparatus has been shown in the drawing as an oscillator or high frequency generator comprising a space discharge device of the axially symmetrical in-line 'type such as a lighthouse tube I I, and a tank circuit or resonant circuit. The resonant lcircuit comprises an outer conductor in the form of a hollow cylinder I2, and an inner conductor or rod I3 which is preferably tubular to facilitate making connections with the lighthouse tube II. In addition, there are a capacitative loading unit I4, which is preferably adjustable for the purpose of tuning, and suitable terminating members such as a disk I5 closing the far end of the hollow cylinder I2 and connected with respect to radio frequency to the inner conductor i3, and av connecting member I6 of suitable shape for electrically connecting the near end of the outer conductor I2 to the lighthouse tube I I.

The lighthouse tube II is not in itself the invention of the present applicants, and such tubes are known to those skilled in the art. Nevertheless, for the sake of clarifying the present invention it may be pointed out that such a tube co-. prises a base Il having conventional prongs I8 for cooperation with a vacuum tube socket (not shown), and certain clectrodesenclosed within the tube II. The electrodes include a cathode, not visible, but having high frequency contact with the base I'I which is in the form of a shell of conducting material, a control electrode or grid, not visible, but having electrical contact with a contact ring I9, and a plate or anode mounted within a contact ring 2 I, and also having a projecting contact 22 for making electrical connections with the radio circuits of the tube I I. For spacing the various contact rings hollow insulating cylinders such las glass cylinders 23 and 24 are provided.

In order'to enable a plate-supply or directcurrent connection to be made to the anode contact 22 through the inner tank conductor I3 without producing a direct-current short circuit to the outer conductor I2, the end plate I is provided with an opening for receiving an insulated contact screw or bolt 25 to which a power supply conductor 26 may be connected. The inner end of the screw 25 is threaded or otherwise secured to a disc 2'! which is joined to the inner tubular conductor I3. In order to complete a low impedance high frequency by-pass connection between the end disc I5 and the inner tubular conductor I3, a second disc 28 connected to the screw 25 is preferably also provided. Suitable insulating members such as an insulating spool, or insulating washers 29 in conjunction with an insulating bushing 3| are provided. The insulating members 29 and 3l may comprise mica, ceramic insulating material, polystyrene or any other suitable, preferably low loss, dielectric substance, which will withstand the operating temperature.

The connecting member I6 is suitably formed so as to make direct electrical connection to the outer conductor I2 and also to the cathode contact or shell I'I of the tube II. Preferably, the end of the inner conductor tube 'I3 toward the tube II and the portion I6 of the member I6 are slitted. or are provided with separate spring contacts in order that good electrical contact may readily be made with the anode contact 22 and the cathode ring or shell I'I when the tube II is inserted in the coaxial line.

The capacitative shunt or load I4 for the tank circuit comprises a cup shaped conductor 32 connected to the inner tubular conductor I3, and a plunger 33 connected to the outer conductor or hollow cylinder I'2. Preferably insulating material is interposed between the plunger 33 and the cup 32 to insure electrical insulation with respect to the direct current power supply circuit. Such insulation may take the form of a ceramic cup 34, or a fabricated insulating cup composed of mica-sheets, or some other suitable low loss dielectric material which will withstand the operating temperatures.

The conducting cup 32 may be connected to the tubular conductor I3 and supported thereby by means of a lug or bracket 35 which is welded, brazed or soldered to the elements I3 and 32.

Preferably the plunger 33 is provided with an adjustable mounting for varying the extent to which the plunger 33 is inserted'into the -cup 32, thereby adjusting the condenser capacity and the resonant frequency of the apparatus. For increasing linearity of the variation in frequency when the plunger 33 is near the maximum capacity position, that is the closest to the inner tubular conductor I3 and the base of the cup 32,'it may be desirable to provide a conical cavity 36 in the inner end of the plunger 33.

Any suitable arrangement may be provided for movably mounting the plunger 33. For eX- ample, a guide member or bushing 31, which is constructed to maintain good electrical contact with plunger 33, may be fitted (preferably soldered) into an opening provided in the side of the outer cylinder I2, and a supporting bracket 38 may be provided which is welded, brazed or otherwise secured to the cylinder I2, and has a threaded opening for receiving an adjusting screw 39 attached to the plunger 33 which is preferably circular` in cross-section if this type of adjustment is employed. In order to secure good electrical conta-ct between the plunger 33 and the bushing 31, a plurality of spring contact fmgers 53 may be provided.

For coupling the capacitative loading element I4 to the grid circuit, a coupling loop 4I is provided which may take the form of a bent piece of sheet metal such as spring brass adapted t0 make direct resilient contact with the grid contact ring I9 at the end 42 of the member 4I, and also electrically coupled with respect to the high frequency circuit to the outer conductor hollow cylinder I2. Preferably, the member 4I is bent in an arc exceeding in order to provide for withdrawal and reinsertion of the lighthouse tube I I.

In order to avoid a direct-current short circuit between the grid contact I9 and the hollow cylinder I2 insulating washers 43 of a suitable low loss dielectric material are preferably provided. For supporting the coupling loop 4I', a screw 44 may be provided which is threaded into the member 4I and passes through an opening in the outer conductor I2, preferably being insulated therefrom by a suitable low loss insulator bushing 45.

Suitable means may be provided for coupling the tank circuit to other circuits or for supplying and withdrawing power. For example, when relatively little energy is to be withdrawn a capacitative probe may be provided comprising a small plate 46 mounted in proximity to the inner tubular conductor I3 and at the end near the lighthouse tube II and having a conductor 41 drawn through a suitable opening 48 in the hollow cylinder I2. However, where relatively large amounts of power are to be withdrawn, an inductive coupling loop 49 is preferably provided which may be mounted as shown in the far end of the space between the inner and outer conducting members I3 and I2. For adjusting the power taken out through the loop 4S it may be rotatably mounted, if desired, in a manner known to those skilled in the art. For simplicity, the loop 49 is merely shown as being connected to inner and outer conductors 5I and 52 respectively of a coaxial line, the outer conductor 52 being threaded into an opening in the hollow cylinder I2.

The capacitative probe 46 may be employed, for example, for supplying an A. V. C. detector when the apparatus is connected as a super-regenerative receiver with automatic gain stablization, and the inductive loop 49 may be employed in connection with such a circuit for receiving micro-wave energy and retransmitting it automatically whenever a signal is received. The invention is not limited, however, to the use of specific high frequency circuits and accordingly suitable circuits for producing automatic gain stabilization of other forms of operation have not been shown, these circuits in themselves being known to those skilled in the art.

It will be observed that the elements i2 and I3 together, if of sufficient length, would alone serve as a concentric line type of tank circuit adapted to oscillate at such a frequency that the total length of the line was a multiple of a quarter wave length of the operating frequency. However, the arrangement illustrated is considerably more compact than would be required if the elements I2 and I3 alone served as the circuit units of a tank circuit or resonant circuit. The capacitative shunt I4 serves to increase the wave length or reduce the natural frequency of the circuits so that operation at approximately 600 megacycles, for example, is obtained with au m' uti the hollow cylinder I2 having a length of only 2 inches Whereas 41/2 to 5 inches length would be required to constitute a quarter Wave of electromagnetic energy with a frequency of 600 megacycles. Furthermore, difficulty has -frequently been encountered heretofore in operating lighthouse tubes with sim-ple transmission line elements connected thereto unless the-length of the line was as great as a half wave length, and a great saving in size by the present construction is therefore apparent. The capacitative shunt I4 permits a very convenient and compact means for adjusting the natural frequency of the apparatus so as to form a readily tuned oscillator. In addition the presence of the shunt I4 near the end of the tank circuit close to the lighthouse tube I I serves to stabilize the circuit and permits efficient feed-back to the grid circuit of t-he tube. Stabilization is further promoted by the fact that materially greater feed-back may be obtained by the arrangement illustrated than by other known means.

It will be observed that by reason of the construction of the tank unit, the oscillator tube II may readily bc inserted or withdrawn for replacement or test purposes.

If the apparatus illustrated is not intended to oscillate and is to be used as an amplifier only, the grid loop 4I may be omitted, or, in any event, decoupled from the capacitive shunt I4.

rIhe capacity 4of the condenser I4 is preferably made relatively large, of the order of 20 micromicro farads, for example, in o-rder to draw relatively heavy current between the center conductor and the cathode conductor of the coaxial line so as to provide good inductive coupling to the feed-back loop 4I.

In accordance with the provisions of the patent statutes the principle of operation of the inven- .tion has been described together with the apparatus now believed to represent the best embodiment thereof, but it is to be understood that the apparatus shown and described is only illustrative and that the invention may be carried out by other arrangements.

We claim:

1. A high frequency generator comprising in combination a lighthouse tube having anode grid and cathode contact rings, a coaxial line having inner and outer conductors connected to the anode and cathode contacts respectively of said tube at the near end, and closed at the far end with respect to radio frequency, an adjustable capacitor at the near end of the coaxial line connected between the inner conductor and the outer conductor, a feed-back loop in inductive relation to said capacitor connected to the grid contact and coupled to the outer conductor of the coaxial line with respect to high frequencies but electrically insulated therefrom with respect to direct current, and meansfor supplying anode voltage to the inner conductor of the coaxial line, said -coaxial line having a length less than one quarter wave for the frequency at which the generator is intended to operate.

2. In combination, an axially symmetrical inline type of space discharge device, and a coaxial line having inner and outer conductors, the space discharge device having anode, controlgrid and cathode contacts, the inner and outer conductors of the coaxial line being connected at the near end to the anode and cathode contacts of the space discharge device and being closed with respect to radio frequency at the far end, a condenser connected between the inner and outer conductors of the coaxial line at the near end, and means for coupling the inductive eld due to the current through said condenser to the grid `clfmtact of the space discharge device.

, A readily demountable high frequency genera or comprising in combination a lighthouse tube having anode, control-grid and cathode contacts, a coaxial line having a length less than a quarter wave for the frequency for which the apparatus is designed and comprising inner and outer conductors connected at the nearer end respectively to the anode and the cathode of the lighthouse tube, and closed with respect to radio frequency at the far end, a condenser connected between the inner and outer conductors at the near end, an inductive feed-back loop in proximity to said condenser comprising a spring conductor mounted upon the inner surface of the outer conductor of the coaxial line and by-passed with respect to high frequency to said outer conductor but insulated therefrom with respect to direct current with a bent portion thereof adapted to make contact with the control grid contact of the lighthouse tube, whereby contact connections with the lighthouse tube may readily be broken by withdrawing the lighthouse tube axially from the coaxial line.

4. In combination, a space discharge device having anode, cathode and control grid contacts, a transmission line connected to the anode and cathode contacts, a condenser connected across the line, and means for inductively coupling the condenser to the grid contact.

5. In combination, an axially symmetrical inline type of space discharge device having anode, control-grid, and cathode contacts, a coaxial line having a length less than a quarter wave of the frequency for which the apparatus is designed having inner and outer conductors respectively connected at the near end to the anode and cathode contacts of the space discharge device, and closed with respect to radio frequency at the far end, a variable condenser connected between the inner and outer conductors of the coaxial line at the near end thereof, said condenser comprising a cup secured to one of the conductors of the coaxial line and a plunger, coaxial with the cup and adapted to t therein in spaced relation thereto, connected to the other conductor of the coaxial line, and means for relatively moving the cup and the plunger in' a direction of their axis for adjusting the frequency of resonance of the coaxial line.

LOUIS W. SCI-IREINER.

EUGENE V. LEONARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,068,991 Kolster Jan. 26, 1937 2,207,846 Wolff July 16, 1940 2,223,835 Smith Dec. 3, 1940 2,235,414 White Mar. 18, 1941 2,272,062 George Feb. 3, 1942 2,285,662 Hutcheson June 9, 1942 2,287,845 Varian et al. June 30, 1942 2,328,561 Lavoie Sept. 7, 1943 2,351,895 Allerding June 20, 1944 2,353,742 McArthur July 18, 1944 2,408,355 Turner Sept. 24, 1046 2,411,424 Gurewitsch Nov. 19, 1946 

